1. Field of the Invention
The present invention is directed to the field of pulse oximetry sensing, and, more particularly, is directed to a sensor for use with pulse oximetry sensing systems.
2. Description of the Related Art
Early detection of low blood oxygen is critical in a wide variety of medical applications. For example, when a patient receives an insufficient supply of oxygen in critical care and surgical applications, brain damage and death can result in just a matter of minutes. Because of this danger, the medical industry developed oximetry, a study and measurement of the oxygen status of blood. One particular type of oximetry, pulse oximetry, is a widely accepted noninvasive procedure for measuring the oxygen saturation level of arterial blood, an indicator of the oxygen status of the blood. A pulse oximeter relies on a sensor attached to a patient in order to measure the blood oxygen saturation.
Conventionally, a pulse oximeter sensor has a red emitter, an infrared emitter, and a photodiode detector. The sensor is typically attached to a patient""s finger, earlobe, or foot. For a finger, the sensor is configured so that the emitters project light through the outer tissue of the finger and into the blood vessels and capillaries contained inside. The photodiode is positioned at the opposite side of the finger to detect the emitted light as it emerges from the outer tissues of the finger. The photodiode generates a signal based on the emitted light and relays that signal to an oximeter. The oximeter determines blood oxygen saturation by computing the differential absorption by the arterial blood of the two wavelengths (red and infrared) emitted by the sensor.
There are at least two general types of sensor devices in use in the pulse oximetry industry. A first type has the red emitter and the infrared emitter connected in back-to-back configuration. That is, the red emitter and the infrared emitters are light-emitting diodes, each of which has a respective anode and a respective cathode. As is well-known in the art, when a sufficient voltage of the proper polarity is applied across the anode and cathode of a light-emitting diode, the light-emitting diode will emit light of a predetermined wavelength (e.g., red light or infrared light). By connecting the light-emitting diodes in a back-to-back configuration, the same voltage source can be applied to both light-emitting diodes. Thus, when the voltage source has a first polarity, one of the two light-emitting diodes is activated to emit light, and when the voltage source has the opposite polarity, the other light-emitting diode is activated to emit light. It can be understood that only two connections are needed from the oximeter system to the light-emitting diodes. (See, for example, U.S. Pat. No. 5,758,644, assigned to the assignee of the present application, and incorporated by reference herein. See, in particular, FIG. 8A of U.S. Pat. No. 5,758,644.) The photodetector can be advantageously connected between one of the two connections and third connection so that both the light-emitting diodes and the photodetector are connected to the oximeter system by only three interconnection wires.
The second type of sensor in general use connects the two emitters in a common electrode configuration. That is, one of the two electrodes of each emitter (e.g., the cathode of each emitter) is connected in common to one connection to the oximeter system. The other electrode (e.g., the anode) of each emitter has a separate connection to the oximeter system, thus requiring a total of three connections for the emitters. The photodetector has at least one extra connection to the oximeter system, thus requiring a total of four connectors for the sensor. (See, for example, FIG. 4A of U.S. Pat. No. 5,578,644.)
Because oximeter systems are generally designed to be used with one of the two sensors described above, its is necessary for a hospital having both types of oximeter systems to stock a supply of three-wire sensors to be compatible with oximeter systems designed for back-to-back emitters and to stock a supply of four-wire sensors to be compatible with oximeter systems designed for common electrode sensors. Although conversion units are commercially available to permit three-wire sensors to be used with four-wire oximeter systems and other conversion units are commercially available to permit four-wire sensors to be used with three-wire oximeter systems, such conversion units are expensive and typically include conversion electronics that must be powered from a separate power supply. Because the conversion units and the required electrical connections for the conversion units are bulky by nature, the conversion units are particularly unattractive in a hospital setting, such as a surgical room.
One aspect of the present invention is an oximeter sensor for use with multiple oximeter systems. The oximeter sensor comprises a first light-emitting diode having an anode and a cathode. The first light-emitting diode emits light of a first wavelength when a sufficient voltage is applied from the anode to the cathode. The sensor further comprises a second light-emitting diode having an anode and a cathode. The second light-emitting diode emits light of a second wavelength when a sufficient voltage is applied from the anode to the cathode. The sensor comprises a photodetector having a first terminal and a second terminal. The photodetector has a measurable characteristic that responds to varying intensities of light incident on the photodetector. The sensor comprises a sensor connector having a first contact coupled to the anode of the first light-emitting diode, a second contact coupled to the cathode of the first light-emitting diode, a third contact coupled to the anode of the second light-emitting diode, a fourth contact coupled to the cathode of the second light-emitting diode, a fifth contact coupled to the first terminal of the photodetector and a sixth contact coupled to the second terminal of the photodetector. In accordance with this aspect of the invention, the oximeter sensor further comprises an interconnector for interconnecting the oximeter sensor with an oximeter system monitor. The interconnector includes a first connector having contacts engageable with the contacts of the sensor connector. The interconnector includes a second connector having contacts engageable with contacts in a connector on the oximeter system monitor. The interconnector electrically connects selected contacts of the first connector to selected contacts of the second connector to electrically interconnect the first light-emitting diode, the second light-emitting diode and the photodetector to the oximeter system monitor. In one embodiment, the interconnector comprises a shell having the first connector on a first end and having the second connector on a second end. In an alternative embodiment, the interconnector comprises a flexible cable having the first connector at a first end and having the second connector on a second end. In one application for use with a five-wire oximeter monitoring system, the interconnector electrically interconnects the first light-emitting diode and the second light-emitting diode in a common anode configuration. In an alternative application for use with a four-wire oximeter monitoring system, the interconnector electrically interconnects the first light-emitting diode and the second light-emitting diode in a back-to-back configuration wherein the anode of the first light-emitting diode is connected to the cathode of the second light-emitting diode and wherein the cathode of the first light-emitting diode is connected to the anode of the second light-emitting diode.
Another aspect of the present invention is an interconnector for interconnecting an oximeter sensor to an oximeter system monitor wherein the oximeter sensor has a sensor connector having contacts electrically connected to the anodes and cathodes of first and second light-emitting diodes and having contacts electrically connected to the terminals of a photodetector. The interconnector comprises a first connector having contacts engageable with the contacts of the sensor connector. The interconnector comprises a second connector having contacts engageable with contacts in a system connector in electrical communication with the oximeter system monitor. The interconnector further comprises electrical interconnections between the first connector and the second connector that electrically connect selected contacts of the first connector to selected contacts of the second connector to electrically interconnect the first light-emitting diode, the second light-emitting diode and the photodetector in a configuration compatible with the oximeter system monitor.